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How to boot on an ISO image from Grub

If you need to use multiple Linux distributions, you do not have so many options. You can either install it, on your machine or in a virtual one, or you can boot on it from an ISO file in live mode. The second option, if less needy in hard drive space, is bothersome as you will need a USB stick or CD to hold the ISO file and boot from. However, there is a third alternative which is a bit of a compromise: have the ISO image on your hard drive, and boot into it in live mode.